Magnetic and atomic order in the potential half metallic ferromagnets Ru_2−xFe_xCrGe

Neutron powder diffraction and magnetization measurements have been used to study the crystallographic and magnetic properties of Ru_2−xFe_xCrGe with x = 0, 1.0 and 1.7. Ru₂CrGe was found to have the Heusler L2₁ structure and to order antiferromagnetically below T_N = 16.5 K to a face centred cubic type 2 structure, propagation vector . Only the Cr atoms carry a magnetic moment, which is oriented perpendicular to the propagation vector and has magnitude 1.45 μ_B at 5 K. Replacement of Ru by Fe causes the alloys to become ferromagnetic with accompanying disorder amongst the Fe, Cr and Ru atoms with only the Ge atoms remaining completely ordered. Both the neutron diffraction data and the magnetization results for the ferromagnetic alloys lead to non-integral values of the magnetic moment per formula unit differing significantly from the 2 μ_B predicted by band structure calculations. The materials can therefore not be expected to display ideal half metallic ferromagnetic properties.